The subject matter disclosed herein relates to power distribution system and, in particular, to varying the operational characteristics of capacitor banks along distribution feeder.
Utilities in various locations are required to deliver power to consumers at a base voltage plus or minus a certain percentage. For example, in the Unites States utilities are required to deliver power to residential consumers at 120 volts plus or minus 5%, which yields a range of 114V to 126V. In Europe, utilities are required to deliver power at 230V plus or minus 10%. It is well known that voltage gradually decreases along distribution feeder lines due to the accumulation of load. To meet the above requirements, one approach is to transmit power with a voltage from a substation at 126 volts to ensure that the last consumer on the line gets at least the minimum standard of 114 volts during peak load. Such transmission, while effective, results in at least some consumers receiving higher than needed voltage which leads to increased energy costs and shortened life expectancy for electrical equipment.
In addition, utilities need to manage reactive power on the distribution feeders. In general, reactive power is “imaginary” power that is created by reactive loads (e.g., loads containing inductive or capacitive elements). Energy storage in the loads results in a time difference between the current and voltage waveforms. During each cycle of the AC voltage, extra energy, in addition to any energy consumed by the load, is temporarily stored in the load in electric or magnetic fields, and then returned to the feeder a fraction of a second later in the cycle. The “ebb and flow” of this nonproductive power increases the current in the feeder. The increased current can reduce the lifetime of components along the feeder.
One approach to offsetting reactive power is to introduce capacitors (typically in the form of shunt capacitor banks) along the feeder. That is, capacitor banks can be used to reduce current throughout the system. In particular, fixed and switched capacitor banks are used as a means of volt-amperes reactive (VAr) management. As part of VAr management, or as a separate endeavor, the capacitor banks can also be used to adjust the voltage profile of voltage along the feeder.
A capacitor bank can be operated in either remote or local operating modes. In a remote mode, a remote control apparatus issues TRIP (open) or CLOSE commands that cause the capacitor bank to be disconnected from (TRIP) or coupled to (CLOSE) the feeder. If a communication loss between the remote control apparatus and the capacitor bank occurs, the capacitor bank typically reverts back to the local operating mode. In a local operating mode, the capacitor bank can automatically connect or disconnect from the feeder based on a predefined criteria (e.g., voltage measured on the feeder, time, VAR, current, outside temperature, etc.). Such operation may be acceptable but can cause voltages on the feeder to change. In particular, if the capacitor has previously been remotely controlled in a manner to allow voltage along the feeder to be kept as low as possible, reverting back to the original settings means higher voltage and, as such, reintroduction of one or more of the problems described above.